Adaptor device for domestic shooting practice with large-calibre hand-guns

ABSTRACT

Improved devices for adapting revolvers for shooting practice with pellets. Advantages include qieter operation, no need of accesories for loading or unloading the primer and a universal size for cylinders of different lengths. A venturi passage separates the detonaing chamber from the bore, thereby accelerating and depressurizing the expansion gases and reducing noise. In one embodiment, the adaptor includes an internal cannon which is longitudinally displaced together with the pellet by the propulsion gasses. Improved adaptors are disclosed for pistols, for selfcentring a barrel liner and protecting rifling grooves.

REFERENCE TO RELATED APPLICATION

[0001] The present application is a continuation of application Ser. No. 08/888,939.

FIELD OF THE INVENTION

[0002] The present invention is related to shooting practice with firearms and concerns a device for enabling large-calibre firearms to be fired with small-calibre missiles or ammunition. The invention particularly concerns an adaptor device for a large-calibre gun for using low-cost and freely-available munition such as air-pellets and pistol primers, utilizing the thrust of the primers to safely fire pellets with a similar degree of accuracy and range but much less kinetic energy in comparison with the standard high-calibre ammunition rounds.

[0003] The adaptor devices of the invention are devised for use on large-calibre guns in places not specially protected as shooting ranges, for instance. Among other uses, the invention allows indoor practice or teaching with rifles, pistols and revolvers, as well as handling collection-item or antique firearm pieces without wearing the barrel out.

BACKGROUND OF THE INVENTION

[0004] Practice with large-calibre firearms in times of peace is restricted to shooting ranges, whereto the shooter has to travel with all the precautions, expense and bother this implies. By no means should firearms such as 9 mm pistols or .38 or .357 Magnum revolvers, for example, loaded with standard-calibre ammunition be fired at home, be it for reasons of practice, training or learning, because of the serious risk of death or injury to the household and the neighbourhood as well as because of the loud noise these guns make when going off.

[0005] For this reason, the guns one may practice with without leaving ones' houses are of the compressed-air type, using 4.5 or 5.5 mm pellets as ammunition and even then taking care. However, using compressed-air guns for shooting practice is a rather poor substitute for those who wish to learn or become abler with a firearm of a larger calibre. The use of compressed air instead of gunpowder and the differences in weight, size and blast backlash between one kind of gun and the other significantly vary the responses and feel one gets from handling guns.

BRIEF REVIEW OF THE PRIOR ART

[0006] The prior art has indulged heretofore in attempting to develop suitable adaptor means using readily available pellets for reduced-calibre missiles and primers as detonators.

[0007] U.S. Pat. No. 4,361,093 to Michael Saxby dicloses an adaptor device for firing pellets with a larger-calibre firearm, such as a pistol, revolver or rifle, using primers. The adaptor comprises a two-part ammunition round including a casing externally shaped as a .38 or larger-calibre round of ammunition for loading in a .38 or larger-calibre pistol or revolver in the same way as an ordinary round of ammunition. The casing has a longitudinal passage housing a tubular insert. A tapered socket is provided behind the insert at the base of the casing for holding a 4.5 mm small pistol primer. The forward end of the insert forms a seat for a .177 or .22 pellet in the casing passage. Saxby suggests that the diameter of the forward portion of the passage be slightly larger than the nominal pellet diameter but slightly smaller than the overall maximum diameter of the pellet, i.e. of the pellet skirt. A narrow flame duct extends through the insert for conveying and moderating the thrust of the primer blast on the pellet when the trigger is pressed and the firing pin of the firearm strikes the primer.

[0008] In some of Saxby's embodiments for pistols and revolvers, the adaptor device further includes a removible barrel liner which is inserted through the muzzle of the gun. The liner is a tubular member provided with an O-ring or resilient means at the breech end and clamping means at the muzzle end, the liner small-calibre bore abutting and naturally aligning with the casing chamber. Suggested clamping means is a split ring or plural collets associated with a threaded fastener which screws on to an extension of the liner. Another embodiment of the adaptor device, for 5.56 mm calibre rifles, is designed without the barrel liner.

[0009] The socket is dimensioned for the primer to snugly fit therein, meaning that the primer has to be push-fitted into the socket. In some of Saxby's embodiments, the socket is formed in the base end of the insert and both are supplied together as a unit. The gun is loaded by first push-fitting the pellet and then the insert forwards into the casing chamber, avoiding the risk of the user pushing primers into position. In another embodiment, the primer is seated against the base end of the insert and the loaded casing may be supplied as a unit.

[0010] U.S. Pat. No. 4,735,009 to Thomas Jett dicloses an adaptor kit which allegely simplifyies Saxby's cartridge casing. The casing is a one-piece insert including a pellet seating on the nose end of the casing passage. This enables loading the pellet through the nose end of the cartridge. Tools are disclosed for assisting in loading the primers and pellets into the adaptor.

[0011] Jett further discloses a liner for mounting with O-rings inside the bore of the hand-gun barrel. Substantial lubrication of the bore and the O-rings is recommended before inserting the liner in the barrel.

[0012] In all the above-cited art, the primer seat is dimensioned for the primer to fit snugly, that is, a certain amount of pushing force is required to place the primer in its proper position. This represents certain drawbacks, not the least of which is the risk of the primer detonating under manual pushing pressure. In fact, Jett suggests placing the primer on a flat surface and pressing the base orifice of the cartridge on to the primer, risking explosion and bodily danger such as loosing a finger.

[0013] Moreover, only primers of a predetermined size may be used with such adaptor devices. Specifically, 5.5 mm large-pistol primers may not be used with a device designed for 4.5 mm small-pistol primers.

[0014] There is also the risk of the primer falling out of the seat and the difficulty in removing a spent primer remains. Jetts's '009 patent suggests a gripping tool for facilitating reloading a primer. It is likewise difficult to safely disarm an unused primer using an inertial bullet puller.

[0015] Jetts's '009 patent is forced to locate the pellet seat right in the nose of the casing, meaning that the pellet skirt is deformed at loading. At firing, the pellet has just begun to accelerate when it leaves the casing. In an application in a revolver, the liner rear end may not abut the cartridge nose end so that firing power is lost as the detonation gases leak out of the liner.

[0016] In pistol applications, the liner abuts the cartridge casing and the latter is of exactly the same length as a standard-calibre ammunition round. There is thus the danger of loading and attempting to fire real ammunition with the liner accidentally left in the barrel, with disastrous consequences. In revolver applications, the ammunition rounds are of fixed length and thus suitable only for revolvers with cylinders of that size; otherwise a gap is left between the forcing cone or tapered breech end of the liner and the casing nose such that the speed of the pellet is rather low to insure that it crosses the gap properly.

[0017] Neither are the prior art liners adaptable to gun barrels of different lengths. I also believe that the liner in Jetts's '009 patent may not withstand explosive pressures and thus be displaced forward during firing. This is because the lubricated O-rings either run easily along the barrel bore such that the liner shifts easily during firing or they are sized so that they press hard enough thereagainst to avoid shifting but making the liner harder to insert.

[0018] The external dimensions of the adaptor cartridges of the prior art are designed to be identical to a standard pistol ammunition round. There is thus a danger in backfiring live ammunition with the liner accidentally in the barrel.

[0019] Other known art but further removed from the present invention include U.S. Pat. No. 3,952,657 to Hans-Joachim Kaltmann, U.S. Pat. No. 4,610,485 to Roland Bertiller and U.S. Pat. No. 4,682,545 to Thomas Jett.

SUMMARY OF THE INVENTION

[0020] A main object of the present invention is an economical and easy-to-use solution to enable both beginners and expert sharp-shooters to practice with large-calibre firearms outside shooting ranges and other special installations and inside inhabited environments such as in ones' own home.

[0021] Another object of the invention is to provide simple means for firing a large-calibre gun with lightweight munition, for reasons of instruction, practice, competition or for using antique gun-pieces without wearing the barrel down, thus preserving its value as a collection item.

[0022] And another object of the invention is to provide a means for shooting practice with large-calibre firearms using low-cost and freely-available ammunition, using detonating means such as a primer having a detonating power substantially less than that of a standard ammunition round.

[0023] An important object of the present invention is a reduced calibre adaptor device which eliminates or substantially reduces the risk of manipulating primers.

[0024] A further object is an adaptor device with means for seating a primer, wherein the latter may not fall out but which the remains thereof are easy to remove once spent or while still active, in particular without recourse to accessory tools.

[0025] And another important object is an adaptor device suitable for primers of different sizes.

[0026] An additional object of the invention is a barrel liner including simple and easy-to-use means to secure and keep it in place during firing.

[0027] Yet another object of the invention is to preclude the risk of firing real ammunition in a pistol or rifle with the adaptor liner left in the barrel.

[0028] A further object of the invention is an adaptor device which may be used with revolvers of different length cylinders.

[0029] Yet a further object of the invention is an adaptor device providing a hermetic seal in revolvers.

[0030] Another object of the invention is to improve the the performance of the adaptor cartridge, in particular providing a retractible insert for increasing the thrust on the pellet.

[0031] Another object of the invention is to reduce the noise heard at primer detonation.

[0032] The present invention essentially comprises an adaptor device. The adaptor comprises a cartridge casing adapted for holding a pellet and a primer in prearranged positions. The adaptor includes an elongated tubular casing having an external shape generally approximating or replicating the standard calibre ammunition round. As defined in claim 1, the casing has: a seat for the primer provided at the casing rear end; a base removibly attached to said casing rear end to retain the primer in the seat, said base provided with an orifice for passage of the firing pin therethrough; a longitudinal bore of a diameter which is that of the reduced calibre, the bore extending from the casing nose end towards a position inside the casing intermediate the rear and nose ends; an inward rim forming a missile seat at the rearward end of the bore and a narrow passageway for passing expansion gases generated by the primer detonating to the missile to propel the munition out of the bore and the firearm barrel.

[0033] The base is preferibly screwable onto the casing rear end after a primer has been placed in the primer seat and unscrewable off the casing rear end to discard spent primer reamins. Other preferred forms are defined in dependent claims.

[0034] In one preferred embodiment, the adaptor device further includes a barrel liner adapted to be pushed into the gun barrel through the muzzle end thereof until it abuts against the nose end of a casing loaded in the chamber. The liner has an external thread partly protruding out of the gun barrel mouth at the muzzle end, a sleeve made from a deformible plastics material and which covers a part of the liner tube after the thread and a nut for screwing onto the thread to tighten against the sleeve until the sleeve expands diametrically to press against the internal wall of the barrel, thereby inmobilizing the liner tube. The liner has at least one O-ring housed in a respective circumpherencial groove adjacent to the rear end of the tube to keep it centred inside the barrel and maintain a gap along the length between the tube and the barrel.

[0035] In a particularly preferred embodiment, the casing houses a longitudinally displaceable cannon containing the longitudinal bore for loading the reduced calibre missile and spring means for urging the displaceable cannon towards the casing rear end, the nose end of the casing including an orifice sixed to enable the cannon to emerge therethrough under the effect of expansion gasses produced by a detonating primer struck by the firing pin. The liner rear end may further be made of a relatively soft plastics material for initially absorbing strikes from a displaceable cannon in the casing until the material becomes sufficiently gorged to abut the cannon in a maximum displaced position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above-stated and other novel features and aspects of this invention and how it may be reduced to practice may be understood better from the following detailed description of a preferred embodiment shown in the attached drawings, wherein:

[0037]FIG. 1 is a longitudinal-cross section of an adaptor device, according to this invention, for a cylinder-type gun, such as a revolver or some large-calibre rifles.

[0038]FIG. 2 is a longitudinal-cross section of an adaptor device, according to this invention, for a fixed-chamber gun, such as a large-calibre pistol.

[0039]FIG. 3 is a longitudinal-cross section of a barrel of a pistol showing the adaptor device therein, according to an improved embodiment of the invention.

[0040]FIG. 4 shows a liner tube of an adaptor device for a revolver, according to an improved embodiment of the invention.

[0041]FIG. 5A shows a first embodiment of a rear tube of the adaptor device for the revolver of FIG. 4. FIG. 5B illustrtaes the embodiment of FIG. 5A in a firing position.

[0042]FIG. 6 shows a second embodiment of a rear tube of the adaptor device for the revolver of FIG. 4.

[0043]FIG. 7 shows a third embodiment of a rear tube of the adaptor device for revolvers.

[0044] Finally, FIG. 8 shows a fourth embodiment of a rear tube of the adaptor device for revolvers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] Describing in detail how the above-stated invention may be put to practice, FIG. 1 shows an embodiment of the adaptor device 11 of the present invention for a revolver, typically (the firearm itself is not depicted in the drawings). The adaptor 11 comprises a tubular body 13 internally traversed by a longitudinal bore 15, preferibly with rifling grooves 17 for increased precision.

[0046] The external diameter of the tube 13 is recessed at its forward part 19 by a step 21 for making a stop against the inlet mouth of of the gun chamber. More precisely, the diameter of the forward part of the tube 13, between the step 21 and the outlet end 23, is that of the standard gun ammunition or bullet whereas the external diameter in the forward part 25 corresponds to the ammunition cartridge.

[0047] The rear end of the tube 13 itself is open, internally recessed and threaded for attaching a primer-holder 27 provided with a base 29 which continues in a circumpherencial flange 31. The base 29 is centrally traversed by a hole 33 extending towards a seat 35 for the primer 37, any of which marketed as “small pistol” o “large pistol” primers may be used. This seat 35 comprises a rear conical cavity, having a diameter decreasing towards the hole 33, and a forward cylindrical cavity, joined to one another, the latter closed in part by a primer retainer 39 formed by a cylindrical member having a central passage 41 coaxially aligned with the inlet end of the bore 15.

[0048] In an application of the adaptor 11 for .44-calibre Magnum revolver, as it is popularly called, the full length of the unit 11 is 41.9 mm, broken down as: 7.8 mm forward length 19, 32.6 mm rear length 25 and 1.5 mm width of the flange 31 at the base 27. The diameters of these three parts are 10.9 mm and 11.6 mm for the front 19 and rear 25 tubular parts, respectively, and 13.1 mm for the base 29, whereas the diameter of the bore 15 is 4.5 or 5.5 mm according to the ammunition 43 to be used, the diameter of the gas passage hole 41 may be 1 mm and that of the seat 35 according to the size of the primer 37.

[0049] To load the adaptor 11, first the three members 13, 27 and 39 are disassembled, unscrewing the base 27 from the tubular body 13 to uncover and take out the primer-latch 39. A conventional pistol primer 37 is placed on the seat 35 through the forward mouth of the base 27 and a pellet 43 or round shot, also conventional, such as of 4.5 or 5.5 mm, is placed in the chamber of the bore 15 through the rear mouth of the latter. The cylindrical primer-latch 39 is replaced again to separate the pellet 43 from the primer 37 and the base 27 is screwed back on to the tube 13.

[0050] The cylindrical member 39 is for retaining the primer 37 in its seat 35 where it may be struck by the firing pin of the gun through the hole 33 when the shooter presses the trigger (not shown). The expansion gasses produced by the detonation flow through the passage 41 and drive the pellet 43 through the latter, thereby producing the shot.

[0051] The basic structure of the embodiment of FIG. 1 requires some changes when the adaptor device of the invention is for use with a gun having a chamber, as is the case of a pistol, for example a .45-calibre ACP pistol. The barrel 75 of the pistol is schematically drawn in FIG. 2 and is internally occupied in its entirety by the adaptor 81 of the present invention. The adaptor 81 comprises a liner tube 83 and a rear base 85. The latter is internally threaded for screwing on the primer-latch 87 which, in turn, is provided with a passage 89 for gasses recessed at its forward part to form a pellet-housing chamber 91.

[0052] The adaptor 81 is pushed into the barrel 75 through the chamber 77 until its outlet-end mouth 93 protrudes through the outlet mouth 79 of the barrel 75, revealing an external thread 95 for affixing a nut 97 for holding the adaptor 81 in place. The tube is further provided with an external circumpherencial groove for housing an O-ring 99 to hold the adaptor 81 fast inside the barrel 75, specially during firing, thereby assisting in the aim of the shot.

[0053] The entire length of the adaptor 81 is at least 127 mm, 11.4 mm of which correspond to the base, the diameter of which is 12 mm. The middle part of the tube 83 which goes inside the barrel 75 of the pistol has a diameter slightly less than 11.4 mm.

[0054] A more preferred embodiment of the invention is set forth in FIG. 3 which schematically shows the barrel 75 of the pistol internally occupied by the adaptor 181 of the present invention. The adaptor 181 comprises an elongated liner tube 183 and a rear tube 187, shorter than the former, screwably closed behind by a base 185. The latter contains a housing for a primer 37. The shape of the combination of the base 185 and the rear tube 187 is similar to a standard-calibre ammunition and includes a circumpherencial recess 201 abutting against a circumpherencial step in the chamber 77 which normally retains a standard ammunition cartridge.

[0055] However, the overall length of the combination 185-187 is advantageously shorter that of standard-calibre ammunition as a means of protection against neglecting to take the liner 183 before shooting with real ammunution.

[0056] The rear tube 187 includes the gas passage 89 recessed at its forward part to form a pellet chamber 91. Gasses coming from a just-fired primer 37 are accelerated and decompressed through this passage, taking advantage of Venturi's principle to provide a silencer.

[0057] The liner tube 183 is pushed into the pistol barrel 75 through the outlet mouth 79 until it abuts against the rear tube 187 loaded in the chamber 77. The oulet mouth 193 of the liner tube is externally threaded 95 and in part protrudes out of the mouth of the gun barrel 75. A nut 197 is then screwed onto the thread 95 to press against a sleeve 203 made from a deformible plastics material and which covers a part of the liner tube 183 after the thread 95. The nut 197 is tightened until the sleeve 203 expands diametrically to press against the internal wall of the barrel 75, thereby immobilizing the liner tube 183.

[0058] The liner tube 183 has two O-rings 199 housed in respective circumpherencial grooves adyacent to the rear end of the tube 183 to keep it centred inside the barrel 75 and, more importantly, maintain a gap between the metallic wall of the tube and that of the barrel 75 which preserves the grooves inside the latter.

[0059]FIG. 4 shows the liner tube 183′ adapted to revolvers for a quieter shot. No accesory tools are needed for loading and unloading the pellet 43. In this embodiment, the second O-ring 199 is replaced by a plastics rear end embodied by a short length of tube 205 made of a material known as “DELRÍN”. The length of the liner tube 183′ is such that the rear end 205 is at a scarce distance, advantageously in the order of a few tenths of a millimetre, from the forward end of the cylinder of the revolver (not illustrated), practically abutting agains the forcing cone of the revolver barrel when the liner tube 183′ is inside the revolver barrel and immobilized by the nut 197 expanding the sleeve 203.

[0060] The elongated liner tube 183′ of FIG. 4, which stays fixed inside the gun during a firing round, is complemented by a second unit of the adaptor device 181′ of the invention, formed by a short tubular member 11′ having an external shape and size similar to standard-calibre ammunition for that gun, as illustrated in FIGS. 5 and 6. This short tubular member 11′, or “pseudobullet” as it could be termed, loads the pellet 43 and the primer 37 for each shot. That is to say, in contrast to the forward tubular member 183′, the rear tubular member 11′ is changed for each shot, by the automatic turn of the cylinder, and has to be reloaded before it may be used again. It may be seen that both members 183′ and 11′ of the adaptor 181′ of the invention carry out different functions in that, respectively, one downscales the dimensions of the gun barrel whereas the other loads ammunition of another calibre.

[0061] Describing in detail the embodiment of the tubular member 11′ shown in FIG. 5, it essentially comprises a tube 13′ having an external diameter which is recessed at its forward part 19 by a step 21 capable of abutting against the chamber inlet mouth of the gun. More precisely, the diameter of the forward part of the tube 13′, between the step 21 and the outket end 23′, is that of the bullet or standard ammunition for the gun whereas the external diameter in the forward part 25 corresponds to the ammunition cartridge.

[0062] The rear end of the tube 13 itself is open, internally recessed and threaded for attaching a primer-holder 27 provided with a base 29 which continues in a circumpherential flange 31. The base 29 is centrally traversed by a hole 33 extending towards a seat 35 for the primer 37, generally any of which marketed as “SMALL PISTOL”, “SMALL RIFLE”, “LARGE PISTOL” or “LARGE RIFLE” primers may be used.

[0063] The interior of the cannon 207 includes a bore 15 extending towards the forward end 23′ of the rear member 11′ and dimensioned for housing the pellet 43. The bore 15 is communicated backwardly with a pasaje 41 coaxial therewith. The bore 15 of the barrel has a recess 208 to reduce the diameter of the rear part to compensate for the barrel moving forward against the plastics end 205 before the pellet exits. The recess 208 further stops the primer from passing through into the pellet chamber under the firing effect, specially when primers 37 of the “SMALL” type are used.

[0064] More precisely, the opening in the forward end 23′ of the tube 13′ is big enough for the cannon 207 to be pushed forward and stick out of the tube 13′. The cannon 207 has a circumpherential shoulder 209 which does not let the tube get completely out of the tube 13′. Furthermore, a spring 211, which is wound around the cannon 207 and has one end resting against the shoulder 209, urges the cannon 207 inside the tube 13′.

[0065] In order to load the rear member 11′, the base 27′ of the tube 13′ is unscrewed, a fresh primer is placed on the seat 35 and the base 27′ is placed back on again. A 4.5 mm pellet 43 or round shot, such as of the type marketed as “GAMO” or “TORCAZ” for example, is seated in the bore 15 through the forward mouth 23′ of the rear tube 13′ and the short tubular member 11′ is inserted in one of the cylinder receptacles, the gun ready for use. In this case, hollow cup-like or “DIÁBOLO” pellets may be used in spite of their greater structural fragility, since part of the energy generated by the gasses in expansion is consumed in forcing the cannon against the spring 211, thereby reducing the power available for accelerating the pellet and, consequently, the destructive effect of the primer charge on this kind of ammunition which could otherwise become beheaded by an excess charge.

[0066] When the shooter presses the trigger (not shown), the firing pin of the gun strikes the primer 37 in seat 35 through the hole 33. The expansion gasses under the effect of the detonation propel the cannon 207 together with the ammunition 43, compressing the spring 211. Part of these gasses cross through the passage 41 and simultaneously accelerate the pellet 43 inside the cannon 207. The cannon 207 is propelled out of the tube 13, through the hole 23′ and strikes against the “DELRIN” material 205 of the long tube 183′. In this manner, a closed system is formed inside the liner tube wherein both the pellet 43 as well as the propellent gasses coming from the primer 37 are impelled. The pellet 43 shoots out of the little cannon 207, thereby producing the shot, and the cannon 207 is retracted thereafter back into the tube 13′ again by the reaction of the spring 211.

[0067] With use, the cannon 207 repetitively strikes the plastics 205 and gradually wears it down with each shot until enough room is made to accomodate the little cannon 207 after some use. The inclusion of the displaceable cannon 207 provides compensation for different cylinder lengths found in revolvers of a same .38 o .357 MAG calibre, thereby providing a universal adaptor system for a given calibre.

[0068]FIG. 6 illustrates an alternative embodiment of the rear tubular member 11″, which features a primer-latch 39′ included between the primer seat 33 and the chamber housing the cannon 207′. The primer-latch 39′ screws on to the same thread that attaches the base 27′. Apart from this, this embodiment of the tubular member posterior 11″ is similar to the one of FIG. 5.

[0069]FIG. 7 ilustrates an alternative embodiment of the adaptor device of FIG. 1 which essentially consists of a rear tubular unit 151 which may operate as an adaptor alone or in combination with the forward tubular unit 183′ depicted in FIG. 4. The object of this embodiment is to replace the displaceable cannon 207 of FIGS. 5 and 6 with a tubular unit 151 of adjustable length, which the user may match to the length of the cylinder of his gun.

[0070] It comprises a base 155 which, at its forward part, features an internal thread 213 for attaching an intermediate tube 215 including a first stretch 41′ of the gas passage. The intermediate tube 215 features in turn an internal thread 217 at its forward part for screwing on the short tube with adjustable penetration, the latter tube featuring the remaining parts of the gas passage stretch 41″ and of the bore 15′ for housing the pellet 43. The set formed by the base 155 and the intermediate tube 215 have diametrical and longitudinal dimensions corresponding to a standard-calibre ammunition cartridge of the gun whereas the forward tip of the pellet-holder tube 157 looks like a bullet of this calibre.

[0071] That is to say that the munition holder 157 is screwed into the intermediate tube 215 until the overall length of the unit assembled by the three members 155, 215 and 157 equals the length of the cylinder (a little less, in fact, to avoid jamming the cylinder). A counternut 219 is further assembled on the external thread of the munition-holder tube 157 and further tightened against the intermediate tube 215 to stop the joint from lossening.

[0072] The base 155 is unscrewed from the intermediate tube 155 for loading the primer 37. The intermediate tube 215 may be integrated into a single piece with the base 155 if a fully-cylindrical seat is provided, such that the primer 37 is held therein by the pressure exerted against the cylindrical sidewalls for enabling the primer 37 to be loaded from behind, through the firing-pin access hole 61.

[0073] Lastly, the alternative embodiment of the rear unit 151′ featured in FIG. 8 supresses the intermediate tube such that the length of the unit is not screwingly regulated. Rather, the length of the munition-holder tube 157′ is sized to the longest cylinder available on the market, such that the user should cut off the forward point 123 of the tube 157′ to the right size if the cylinder of his gun is shorter.

[0074] Of course, changes, variations and aggregations may be made to any of the above-detailed embodiments, without departing from the scope nor the spirit of the invention. The same has been described by way of preferred embodiments, however those skilled in the art may suit it to other applications or introduce modifications without departing from the purview of the invention as set forth in the appended claims. For example, the base 29, 55, 85 may be press-fitted into the tube 13, 57, 83 instead of screwed onto the latter. 

I claim:
 1. An adaptor device for firing a gun of a predetermined calibre loaded with a missile of a reduced calibre, said gun including a barrel with a large-calibre interior diameter, a firing chamber of a similar diameter and axially aligned with said barrel and designed to hold a standard-calibre ammunition round and firing means including a firing pin for impinging into the rear part of said chamber for firing the gun, wherein the adaptor device includes an elongated tubular casing (11) having an external shape generally approximating or replicating said standard calibre ammunition round, said casing having: a rear end and a nose end, the latter for pointing towards the barrel muzzle of the gun, a seat (36) for said primer provided at said casing rear end, a base (27) removibly attached to said casing rear end to retain said primer in said seat, said base provided with an orifice (33) for passage of said firing pin therethrough, a longitudinal bore (15) of a diameter which is substantially that of said reduced calibre, said bore extending from said casing nose end towards a position inside said casing intermediate said rear and nose ends, an inward rim forming a missile seat at the rearward end of said bore, and a narrow passageway (41) for passing expansion gases generated by said primer detonating to said missile to propel said munition out of said bore and the firearm barrel.
 2. The adaptor device of claim 1, wherein said base is screwable onto said casing rear end after a primer has been placed in said primer seat and unscrewable off said casing rear end to discard spent primer reamins.
 3. The adaptor device of claim 1, wherein said primer seat comprises a cavity including a rear conical portion having a diameter decreasing towards said orifice and a forward cylindrical portion, and wherein said missile seat rim is formed by a removible primer retainer cylindrical member longitudinally traversed by said narrow passageway coaxially aligned with said bore.
 4. The adaptor device of claim 3, wherein said position at one end of said bore comprises a circumpherencial step between said bore and said rear end cavity forming a seat for said primer retainer member.
 5. The adaptor device of claim 1, wherein the length and the external diameter of said casing including said base are substantially those of the large-calibre munition of said firearm.
 6. The adaptor device of claim 1, wherein the length of said casing including said base is substantially shorter than the length of the large-calibre munition of said firearm.
 7. The adaptor device of claim 1, wherein said base includes a circumpherencial flange.
 8. The adaptor device of claim 1, further including a barrel liner (183) having a length which is substantially that of said barrel and a longitudinal bore of a diameter which is substantially that of said reduced calibre.
 9. The adaptor device of claim 8, wherein said liner is adapted to be pushed into the gun barrel through the muzzle end thereof until it abuts against said nose end of a casing loaded in the chamber.
 10. The adaptor device of claim 9, wherein said liner has: an external thread (95) partly protruding out of the gun barrel mouth at said muzzle end, a sleeve (203) made from a deformible plastics material and which covers a part of the liner tube after the thread and a nut (197) for screwing onto the thread to tighten against said sleeve until said sleeve expands diametrically to press against the internal wall of the barrel, thereby immobilizing the liner tube.
 11. The adaptor device of claim 9, wherein said liner has at least one O-ring (199) housed in a respective circumpherencial groove adjacent to the rear end of the tube to keep it centred inside the barrel and maintain a gap along the length between the tube and the barrel.
 12. The adaptor device of claim 1, wherein said casing houses a longitudinally displaceable cannon containing said longitudinal bore for loading said reduced calibre munition and elastic means for resiliently urging the displaceable cannon towards said casing rear end, the nose end of said casing including an orifice sixed to enable said cannon to emerge therethrough under the effect of expansion gasses produced by a detonating primer struck by said firing pin.
 13. The adaptor device of claim 12, wherein said elastic means is a spring wound around the displaceable cannon.
 14. The adaptor device of claim 8, for revolver-type firearms, wherein said casing includes a longitudinally displaceable cannon and said liner has a rear end of a relatively soft plastics material for initially absorbing strikes from a displaceable cannon in said casing until said material becomes sufficiently gorged to abut said cannon in a maximum displaced position.
 15. The adaptor device of claim 1, for revolver-type firearms, wherein said base is adapted to be screwed into or onto said casing to a variable degree to enable the length of said adaptor device to be adjusted to the length of the cylinder of the revolver.
 16. The adaptor device of claim 15, wherein said casing further includes a forward tubular member containing said casing nose end, an intermediate member adjustably screw-coupled between said forward member and said base for adjusting the length of said adaptor device to said length of said revolver cylinder, and a counternut for mainting said adaptor device length.
 17. The adaptor device of claim 1, for revolver-type firearms, wherein said casing nose end is adapted to be cut down to adjust the length of said adaptor device to the length of the cylinder of the revolver. 